The invention relates to the method of production of D-arabinose by direct electrochemical degradation oxidation of a salt of D-gluconic acid.
D-arabinose is an important monosacharide utilized primarily for production of D-ribose in the synthesis of vitamin B2, as a starting material in the production of arabinoxine, as culture medium, etc.
D-arabinose may be prepared by chemical or electrochemical methods causing shortening of the carbon chain by degradation oxidation of D-gluconic acid or its derivatives. A most frequent method utilizes hydrogen peroxide and the catalytic effect of ferric ions (H. C. Fletcher, H. W. Dichl, C. S. Hudson: J. Amer. Chem. Soc. 72,4546, 1950). Industrially best developed method makes use of the oxidation degradation of sodium D-gluconate by the solution of sodium hypochlorite in acid solution (Wolf R., Merck Patent GmbH Federal Republic of German 2,923,267 (1980), 2,923,268 (1980), Eur. Pat. Appl. 20,959 (1981)). Substantial disadvantage of chemical methods utilizing oxidizing agents in at least stoichiometric amount is the high costs of subsequent separation of e.g., 1.5 kg of NaC1 per 1 kg of d-arabinose produced during hypochlorite oxidation, or separation of cupric ions, whose presence is intolerable for pharmaceutical production of vitamin B2.
Indirect electrochemical degradation oxidation of D-gluconic acid requires, in comparison with the chemical methods, only a fraction of the stoichiometric amount of the oxidizing agent electrochemically regenerated during the reaction. Use of ceric salts for indirect oxidation is subject of Japanese patent Nos. (58-39695 (1983), 56-013613 (1981)). A drawback of this method is the costly separation of ceric salts from the product and very low specific production capacity of conventional plate electrolyzers.
This drawback becomes even more manifest in case of direct electrochemical degradation oxidation of D-gluconic acid. In the literature presented results (G. W. Hay, F. Smith, J. Can. of Chem. 47 (1969)417) of direct degradation oxidation of D-glucose in nonaqueous solution indicate only 12.4% of D-arabinose and low selectivity of the reaction. The low yield of this slow reaction is the consequence of small electrode area of the conventional parallel plate laboratory electrolyzer and low current denisty admissible for the given reaction. From the standpoint of industrial utilization this method in conjunction with the conventional electrolyzers is economically unfeasible.
Low interfacial area of electrodes per unit volume of the conventional plate electrolyzers leads in industrial practice to voluminous apparatuses and high investment costs. Also the running costs and the costs of subsequent separation of D-arabinose are high due to the very low yield and selectivity of the reaction.